yeah you are right. on average the tahiti chips can match or slightly exceed their Kepler counterparts clocked at a 100 mhz higher.
HD 7970(1.1 Ghz) = HD 7950(1.15 Ghz) = GTX 680(1.2 Ghz) = GTX 670(1.25 Ghz)
Whats disappointing is AMD decided to skip a Pitcairn and Tahiti refresh. A Bonaire like refresh would have brought competition to the GTX Titan and GTX 780 and much better prices. Hopefully AMD's Volcanic Islands refresh comes out in Oct 2013 and brings much needed competition to the high end GPU market.
I think the problem is that High End GPUs constitute a very small part of the market. AMD's got a LOT on it's plate with 3 brand new consoles. As we've seen before, almost all of the GPUs you've listed, 7970, GTX 680, GTX 670, and Titan, all constitute below 3% of the users of graphics cards.
I know you're looking at it from a high end "We need to beat nvidia" but from a monetary perspective, AMD is looking to make as much money as possible. In that case, I can see why AMD would simply go with a rebrand for the 8000 series. The 700 series is going to be released at a price premium lets be real, that's what Nvidia does. On a price to performance level, where the MAJORITY of the market spends it's money, AMD will probably still win and still make good profits. Actually better profits since they're selling last years stuff this year.
High End GPU competition is great for us. It's great for reviewers, it's great for gaming forums, it's great for serious gamers. For the masses though and for AMD, they care in that for some reason, people like to know that you have "THE BEST CARD", but AMD will be willing to lose that battle if it means they make more money, which right now I think they will.
